Determination of oxygen in titanium and titanium alloys



Jan. 17, 1956 M. CODELL ET AL DETERMINATION OF OXYGEN IN TITANIUM ANDTITANIUM ALLOYS Filed Dec. 10, 1954 SMMV INVENTORS MAURICE CODELL BYGEORGE NORW/TZ WfWdMQw m QM4fidm ATTORN 5- United States Patent fi2,731,330 Patented Jan. 17, 1956 ice DETERMINATION OF OXYGEN IN TITANIUMAND TITANIUM ALLOYS Philadelphia, Pa, America as repre- Maurice Codelland George Norwitz,

assignors to the United States of sented by theSecretary of the Army Theinvention described herein may be manufactured and used by or for theGovernment for governmental pur poses without the payment of any royaltythereon.

This invention relates to a method for quantitative determination ofoxygen in titanium and its alloys. The ductility, hardness and grainstructure of titanium and its alloys are influenced materially by oxygencontent and for that reason quantitative determination of containedoxygen is of the utmost technological importance.

Oxygen in titanium and its alloys has been determined by a vacuum fusionmethod. According to this method a sample is fused in the presence ofcarbon. The oxygen is "converted to carbon monoxide which is thenoxidized to carbon dioxide. Two techniques are employed. In one, a lowmelting point alloy of the sample and iron is formed; in the other, alow melting point alloy of the sample and tin is formed. Both techniquesrequire expensive apparatus and highly trained technicians. Anadditional disadvantage is that when certain alloying elements arepresent in a sample, e. g., manganese, such elements volatilize uponfusion of the sample, condense downstream in the apparatus train, andmay recombine with the oxygen to vitiate results.

Another known method is that of chlorination. According to this methoddry chlorine is passed over the sample at 400 C.; the titanium isvolatilized as titanium tetrachloride and the oxygen remains as titaniumdioxide. The oxygen is then calculated by determining the titanium ofthe titanium dioxide colorimetrically. in this method a correction mustbe made for carbon in the sample in view of the reaction wherebycontained oxygen is lost as carbon monoxide. The chlorination reactionmust be controlled carefully to avoid low results which are caused byattack of chlorine upon titanium dioxide, with attendant production ofgaseous (free) oxygen. Another characteristic of this method that mayproduce low values is that when certain metals such as molybdenum arepresent in a sample, oxygen is lost as oxychloride. Dry hydrogenchloride can be used in lieu of chlorine; in any event, values obtainedby chlorine and hydrogen chloride volatilization techniques are in pooragreement with values obtained by vacuum fusion analyses.

Oxygen in titanium but not in its alloys has been determined alsothrough the phenomenon of additive hardening effects of oxygen andnitrogen. Given Brinell hardness and nitrogen content, oxygen content isdeterminable.

Additional methods are: By radioactivation wherein the specimen issubjected to fast neutron bombardment for 30 seconds followed byobservation of activity after a known time interval, based upondetection of approximately 6.1 to 7.1 mev. gamma activity with ahalf-life of 7.35 seconds resulting from the O (n,p)N reaction; thismethod requires a series of calibrated titanium specimens of knownoxygen content. By means of the mass spectrometer wherein a known amountof O tracer is added to the sample; the oxygen is extracted by vacuumfusion as carbon monoxide, and the ratio 0 to O is established. Bydifference, in oxygen-titanium alloys containing rather large amounts ofoxygen and only insignificant amounts of other elements, wherein thesample is oxidized to titanium dioxide by igniting in oxygen, or thetitanium itself is determined volumetrically.

Attempts have been made to determine oxygen-in titaniumspectrographically through the phenomenon of emission of characteristicTiO spectral bands when titanium is sparked in a vacuum; so far themethod has proved of limited value. Suggestions have been made thatoxygen in titanium might be determined with fluorine or non-aqueoushydrogen fluoride. Using fluorine at elevated temperatures, the oxygenprobably would be converted to gaseous oxygen and using hydrogenfluoride under like conditions, the oxygen probably would be convertedto Water. It is known that fluorine attacks titanium at C. Non-aqueoushydrogen fluorde attacks titanium only very slightly at room temperatureand reacts so slowly with titanium oxide at 550 C. that volatilizationis still incomplete after two hours. Apparatus for fiuorinationtechniques would need to be constructed of special materials, possiblynickel. It is another disadvantage that commercial fluorine andnon-aqueous hydrogen fluoride always contain respectively some oxygenand some water. A method for determination of oxygen in titanium oxideand other oxides by the use of bromine trifiuoride has been described.According to preliminary work, the method is applicable to determinationof oxygen in titanium metal. However, certain elements in titaniumalloys appear to present difliculty.

Oxygen in steels, iron powder, bismuth and copper is determined byreduction with hydrogen. This is impracticable with titanium. Ontreatment with hydrogen, titanium absorbs hydrogen with the result thatthe contained oxides are merely reduced to lower oxides. Solution andelectrolytic techniques, frequently used in the case of steels, wherebythe metal is dissolved and the oxide remains, are inapplicable totitanium for the reason that the oxides present in the latter dissolvenearly as readily as the metal itself. Because titanium does notamalgamate, amalgamation techniques used to determine oxygen in sodiumand lead, whereby the metal is amalgamated and the oxide remainsunattached, are inapplicable. For the reason that titanium has nearly asgreat an afiinity for oxygen as it has for aluminum, the method ofmelting with metallic aluminum and then determining the aluminum oxideformed, as is used in the case of steels, is inapplicable. On meltingaluminum with a titanium alloy containing oxygen, an alloy of titanium,oxygen and aluminum is formed by the oxygen remains tied to thetitanium.

The method of our invention comprises conversion of the metal oftitanium and its alloys to metallic bromides and the oxygen to carbonmonoxide. More particularly our method comprises: reaction of titaniumor its alloys, in the presence of carbon in excess of stoichiometricquantity, with bromine vapor introduced into the reaction by a purified,inert carrier gas; separation of reaction products to isolate oxygen ascarbon monoxide; conversion of carbon monoxide to carbon dioxide; andmeasurement of oxygen as carbon dioxide. The equation of the reaction isbelieved to be:

Our method will be described according to its three principal phases andcorresponding zones of apparatus train. These are:

1. Purification of carrier gas in a gas purification zone. 2. Reactionof sample with bromine vapor in presence of carbon in a reaction zone.

'rier gas is charged with bromine vapor.

Accordingly, with reference to the diagram forming a part of thisapplication, an inert carrier gas, e. g., U. S. Army Class A helium, isreleased from a container 1 by a needle valve 2 through a flow meter 3whereby rate of flow of the gas may be observed and adjusted. Apreferred flow rate is about 130 milliliters per minute. The illustratedflow meter is a mercury manometer type; the mercury is illustrated at 4.A mercury blow-ofi valve 5 is next inserted in the apparatus train as asafety measure against build-up of hazardous pressure. Thence, the gaspasses through a tube 7 containing copper turnings 1i) upstream andcopper oxide 11 in wire form downstream. In this tube which in turn iscontained in an electric heater 6 and sealed from the atmosphere byrubber stoppers at both ends as at numeral 8, the carrier gas ispurified of contained oxygen in passing over the copper turnings, andcarbon monoxide, hydrogen and hydrocarbons are converted to carbondioxide and water in passing over the copper oxide. Glass wool 9 is usedat both ends of tube 7 to holdreagents in place. From the tube 7 whichis maintained at a temperature of 500 C., the gas passes to a dryingtower 12 and therein successively through glass wool 9, sodiumhydroxide-on-asbestos 13, anhydrous magnesium perchlorate 14 and againglass wool, for removal of carbon dioxide, sulphur dioxide and water.The foregoing constitutes the purification-of the-carriergas-phase andcorresponding zone of apparatus train.

Through a washing bottle 15, sealed with a ground glass joint 16 andarranged as a safety trap to protect against a reversal of flow, thepurified gas passes by way of a ball-joint type connection 17 throughbromine 19 and supernatant 98% sulphuric acid 20 in a second 'washingbottle 15. A by-pass of the bromine and sulcarrier gas to a point ofequilibrium prior to each determination. In passing through the brominethe car- In passing through the sulphuric acid the bromine is relievedof traces ofmoisture. The bromine is thus introduced into 21 andsituated in a heater equipped with a pyrometer 26, Within the reactiontube 22 the sample in admixture with carbon is contained in a boat 24which may be of gold, platinum or silica.- at 8-15 C. and is continueduntil conversion of the entire; sample has been attained as evidenced bya disappearance of cloudiness in the vapors efiiuent from the reactiontube. The foregoing constitutes the reaction phase and correspondingzone of apparatus train.

Theproducts of reaction emanating from tube 22 are passed 11110 anErlenmeyer trap ZSwhich -iscooled moderately with ice-water contained intray 29 so as to achieve partial condensation of metallic bromides andbromine. Thefiow continues from side arm 23 successively through twocylindrical traps 31 havinginlet tubes 32 widened at their lowerextremities. The first of the traps is shallowly cooled with a DryIce-in-alcohol bath-34-contained in a beaker 33; the second trap ismore. deeply; immersed ing the same. refrigerant which is also containedin a beaker 33. By means-of the traps 28and 31, the metallic bromidesand bromine are condensed and frozen out. The widened extremities ofinlet tubes 32 avoided occlusion by frozen products. Through a thirdcylindrical flask 31, serving as a bubbler for observing rate of flow atthat point in the apparatus trainandcontaining. sulphuric acid 20, theuncondensed produets :flo .v intoasecond drying tower l2'containingglass wool 9, sodium hydroxide-on-asbestos 13,- anhydrous magnesium.perchlorate 14 anda second layer of-vglass wool. Again, thefunctionofthe glass wool is to hold reagents in place. In this second dryingtower sub- The reaction is carried out 4 stances having acidicproperties are removed by the sodium hydroxide, and the resultant waterof reaction by the anhydrous magnesium perchlorate. Thence the flow isthrough a tube 35 situated in a heater 36, and containing granulatedsilver 37. Tube 35 is maintained at a temperature of 600 C. The lasttraces of brominated carbon compounds are removed by the silver in thistube. The efiiuent of tube 35 which consists of carbon monoxide andpossibly hydrogen liberated from the sample is passed through tube 38positioned in heater 39 and containing copper oxide 11 in wire form.Tube 38 is maintained at a temperature of 500 C. The carbon monoxide andhydrogen are converted herein to carbon dioxide and water which pass toa third drying tower 12 containing anhydrous magnesium perchlorate 14supported by glass wool 9. The water is removed, leaving only carbondioxide and the inert carrier gas to enter an absorption. bulb orweighing bottle 40. The reagents in bottle 40 are sodium hydroxide onasbestos 13 for absorption of carbon dioxide by conversion to sodiumcarbonate, and anhydrous magnesium perchlorate 14 for absorption of thewater produced in absorbing the carbon dioxide. The weighing bottle isexhausted to atmosphere through a safety trap 41 and final bubb'ler 42containing sulphuric acid 20. The foregoing constitutes the separationand conversion phase and corre sponding zone of apparatus train. 7

According to our method acarbon blank is deducted. The blank which is ofamagnitude of 0.9 milligram of carbon dioxide per hour (equivalent toabout 0:33 milligram of oxygen per hour) is consistent and reproducible. It is obtained by passing bromine over 1 .5' grams of heatedcarbon for three hours. Typical hourly blank readings obtained areas-follows:

Average hourly blank for 3 runs 0.88 mg.

Standard deviation for all hourly blanks- 1.08 mg.

A preferred practice of our method comprises preparation 0f a'sample bydrilling, chipping or st'rippinginto pieces of about 0.02 inchthickness. The pieces of sample are then' cleaned with carbontetrachloride and dried thoroughly in an oven at 40 0. Two grams ofsample and 1.5 grams of graphite.powder-, by way of example, are thenplaced in a boat; half the graphite powder is first placed in the bottomof the boat, the sample is then placedthereon and'the balance of thegraphite is usedto cover the sample. 7

The silver. utilized in the separation of last'traces of:

b'rominated hydrocarbons is specially. prepared; 450" grams of silvernitrate are dissolved'in asolution of10 milliliters of concentratednitric acid in 3.5 liters of, water.

A copper tube or'a thick sheet of copper rolled into tubunatant'liquidisthen decanted. The silver is then'was'h'ed" several times with' dilutenitric acid approximately. '1 paif' of concentrated acid to 200 partstapwater) and"thereafter washed with dilute ammoniumhydroxide"(approximately 1 part'of concentrated ammonium"hydroxide"to'l0-parts tap 'water) until the bluecopperamine'color is" noldngerpcrceptibl. Finaliy'the silver is washedsev cral ti-rneswith tapwater, placed in atrayj'andoven 'dried The silver is then"spreadjthinly' at C1 for 1 hour. in porcelain-dishesand baked at 750 C.for l near:

Aftericooling, the silver=is handcrumbled,- and-charged into tube 35 asfollows: A wad of glass wool is inserted into one end of the tube. Thewadded end of the tube is supported on a thick glass rod so as to holdthe wad in place during packing. The silver is inserted through theopposite end of the tube in small portions that are successivelycompressed with a steel rod 0.2 inch in diameter and a tapping hammer.Care must be exercised not to pack the silver so tightly that flow ofgas therethrough would be prevented. Upon completion of the packingoperation, the glass wool wad is removed.

Certain precautions must be observed in the practice of our method.Leaking connections between elements of the apparatus train must beavoided. Leakage upstream of the reaction tube 22 can produce resultsthat are high, and leakage downstream of the reaction tube can causevery low results. Connections upstream of the reaction tube should betested with ammonium hydroxide which when brought close to a leakingconnection will form a white cloud of ammonium bromide. Downstream ofthe reaction tube, connections should be tested with soap solutionwhich, upon completion of testing, is rinsed off with water from a washbottle. The bubbler should be watched as an indicator of leakage in theapparatus; any fluctuation or faltering in bubble rate is indicative ofleakage. To achieve a leak-free laboratory apparatus train, it isessential that ground-glass joints, ball joints and stop-cocks be groundtogether with a paste made of 600 mesh carborundum and water. Allstopcocks should be lightly coated with a fluorinated hydrocarbon typegrease. The weight of carbon dioxide recovered in the weighing bottle 40having been determined, the percent oxygen content of the sample iscomputed according to the equation:

where:

W=Weight of CO2 (grams) B=Blank (grams CO2 per hour) T=Time for run(hours) M =Weight of sample (grams) The results obtained by our methoddiffer on the average only 0.007% from results obtained with the vacuumfusion method. The reproducibility and reliability of our method arereflected by an average standard deviation in results of 0.009%.

We claim:

1. A process for quantitative determination of the oxygen content oftitanium comprising: purification of an inert gas by successive contactwith copper, copper oxide, sodium hydroxide and anhydrous magnesiumperchlorate; saturation of the purified gas with bromine vapor bypassing said gas as a carrier through liquid bromine; dehydration of thebromine vapor by conducting the bromine-saturated gas throughconcentrated sulphuric acid; reaction of the bromine with asampleimrnersed in carbon in excess of stoichiometric quantity byconducting the bromine-saturated gas over the sample; separation fromthe products of reaction of metallic bromide and unreacted bromine bycondensation in a first separation step; separation from the products ofreaction of brominated carbon compounds by passing over silver in asecond separation step; conversion of the remaining products of reactionto carbon dioxide and water by passing over copper oxide; removal of thewater by passing through anhydrous magnesium perchlorate; and collectionof the carbon dioxide as sodium carbonate and water by passing throughsodium hydroxide and anhydrous magnesium perchlorate.

2. A process for quantitative determination of the oxygen content oftitanium alloys comprising: purification of an inert gas by successivecontact with copper, copper 6 I oxide, sodium hydroxide and anhydrousmagnesium perchlorate; saturation of the purified gas with bromine vaporby passing said gas as a carrier through liquid bromine; dehydration ofthe bromine vapor by conducting the bromine-saturated gas throughconcentrated sulphuric acid; reaction of the bromine with a sampleimmersed in carbon in excess of stoichiometric quantity by conductingthe bromine-saturated gas over the sample; separation from the productsof reaction of metallic bromides and unreacted bromine by condensationin a first separation step; separation from the products of reaction. ofbrominated carbon compounds by passing over silver in a secondseparation step; conversion of the remaining products of reaction tocarbon dioxide and water by passing over copper oxide; removal of thewater by passing through anhydrous magnesium perchlorate; and collectionof the carbon dioxide as sodium carbonate and water by passing throughsodium hydroxide and anhydrous magnesium perchlorate.

3. A process for quantitative determination of the oxygen content oftitanium comprising: purification of an inert gas at a rate of aboutmilliliters per minute by successive contact with copper and copperoxide maintained at about 500 0., sodium hydroxide and anhydrousmagnesium perchlorate; saturation of the purified gas with bromine vaporby passing said gas as a carrier through liquid bromine; dehydration ofthe bromine vapor by conducting the bromine-saturated gas throughsulphuric acid; reaction of the bromine with a sample immersed in carbonin excess of stoichiometric quantity and maintained at about 815 C., byconducting the bromine-saturated gas over the sample; separation fromthe precincts of reaction of metallic bromide and unreacted bromine byprogressive exposure to refrigerant at from about 0" C. to about minusC.; separation from the products of rection of brominated carboncompounds by passing over silver maintained at about 600 0; conversionof the remaining products of reaction to carbon dioxide and water bypassing over copper oxide maintained at about 500 C. removal of thewater by passing through anhydrous magnesium perchlorate; and collectionof the carbon dioxide as sodium carbonate and water by passing throughsodium hydroxide and anhydrous magnesium perchlorate.

4. A process for quantitative determination or" the oxygen content oftitanium alloys comprising: purification of an inert gas at a rate ofabout .130 milliliters per minute by successive contact with copper andcopper oxide maintained at about 500 0, sodium hydroxide and anhydrousmagnesium perchlorate; saturation of the purified gas with bromine vaporby passing said gas as a carrier through liquid bromine; dehydration ofthe bromine vapor by conducting the bromine-saturated gas throughsulphuric acid; reaction of the bromine with a sample immersed in carbonin excess of stoichiomctric quantity and maintained at about 815 C., byconducting the brominosaturated gas over the sample; separation from theproducts of reaction of metallic bromides and unreacted bromine byprogressive exposure to refrigerant at from about 0 C. to about minus170 C.; separation from the products of reaction of brominated carboncompounds by passing over silver maintained at about 600 C.; conversionof the remaining products of reaction to carbon dioxide and water bypassing over copper oxide maintained at about 500 C. removal of thewater by passing through anhydrous magnesium perchlorate; and collectionof the carbon dioxide as sodium carbonate and water by passing throughsodium hydroxide and anhydrous magnesium perchlorate.

References Cited in the file of this patent Titanium Barksdale, page 85,The Ronald Press Co. (1949).

4. A PROCESS FOR QUANTITATIVE DETERMINATION OF THE OXYGEN CONTENT OFTITANIUM ALLOYS COMPRISING: PURIFICATION OF AN INERT GAS AT A RATE OFABOUT 130 MILLILITERS PER MINUTE BY SUCCESSIVE CONTACT WITH COPPER ANDCOPPER OXIDE MAINTAINED AT ABOUT 500* C., SODIUM HYDROXIDE AND ANHYDROUSMAGNESIUM PERCHLORATE; SATURATION OF THE PURIFIED GAS WITH BROMINE VAPORBY PASSING SAID GAS AS A CARRIER THROUGH LIQUID BROMINE; DEHYDRATION OFTHE BROMINE VAPOR BY CONDUCTING THE BROMINE-SATURATED GAS THROUGHSULPHURIC ACID; REACTION OF THE BROMINE WITH A SAMPLE IMMERSED IN CARBONIN EXCESS OF STOICHIOMETRIC QUANTITY AND MAINTAINED AT ABOUT 815 * C.,BY CONDUCTING THE BROMINE-SATURATED GAS OVER THE SAMPLE; SEPARATION FROMTHE PRODUCTS OF REACTION OF METALLIC BROMIDES AND UNREACTED BROMINE BYPROGRESSIVE EXPOSURE TO REFRIGERANT AT FROM ABOUT 0* C. TO ABOUT MINUS170* C.; SEPARATION FROM THE PRODUCTS OF